Oil well microwave tools



23, 1965 o. B. HAAGENSEN 3,170,519

011. WELL MICROWAVE TOOLS 3 Sheets-Sheet 1 FIG 2 a 21 HEAT 37 EX CHANGER MAGNETRON 38 MAGNETRON 38 MAGNETRON 3 INVENTOR DUANE B. HAAGENSENBY M ATTORNEY Feb. 23, 1965 D13. HAAGENSEN OIL WELL MICROWAVE TOOLS 3Sheets-Sheet 2 Filed May 11, 1960 INVENTOR HAA G ENSEN ATTORNEY 23,3965D. B. HAAGENSEN 3,170,519

OIL WELL MICROWAVE TOOLS Filed llay 11, 1960 1 s Sheets-Sheet a F 1 r Dc95 u $111 I l SUPPLY f I I H I I I HEATER V VOLTAGE I SUPPLY 1 I 62 L 97-F/6T 6 I L40 9a J"L S I l I l 7 I l l Ll l l/VVE/VTOI? DUANE B.HAAGE'NSEN ATTORNEY bearing formation and United States Patent ()flice 73,110,519 OIL WELL MICROWAVE TOOLS mesne assignments, to Gordon L.Allot, D.C., Cortlandt S. Dietler, Denver, Colo., and Robert E.Sonnelsson, Wellesley, Mass., trustees Y FiledgMay ll, 1960, Ser. No.28,340 10 Claims. (Cl. 166-60) This invention relates generally to therecovery of troleurn products from subsurface reservoirs and, more,

particularly, to the use of high-frequency energy to enhance therecovery of said products, especially with reference to depleted orpartially depleted wells.

The recovery of oil or other petroleum products from subsurfacereservoirs is conventionally accomplished by sinking wells tooil-bearing strata and allowing the natural pressures Within theoil-productive formation to force the fluid into the well bore where itcan be conveniently collected. In some oil reservoirs and partiallydepleted reservoirs theremay not be suflicient. natural pressureavailable to force the oil into the well bore at a sufficient rate tobe. economically profitable.

When such methods can no longer, .be used to effect an economical rateof recovery, secondary recovery methods, such as the injection of water,gas, air, or a combination of these materials into the formation toincrease the pressure, are often used. Other methods which have beenutilized include the application of heat energy to the formation byeither chemical or electrical means or by the direct firing of the oilor gas-bearing regions. The effect of these heating processes is toreduce the viscosity of the fluid and, thereby,,increase the rate offluid flow in accordance with Darcy's law reproduced below:

g KAdP dT ndL whereinis the rate offluid flow, A is the averagecross-sectional area of the permeable formation, K is the permeabilityof theformati'on, dP is the diflerential pressure causing. differencedL,

the fluid to flow through the differential and is the viscosity of thefluid.

Direct firing methods have been found to, produce contamination of thecrude petroleum or gases that are present. Chemical heating methods havegenerally been unable to provide a suflicient amountof heat forsatisfactory results. Electrical resistance heating methods have provedunsuitable in that the transfer of heat to the.

oil-bearing strata is primarilyaccomplished by conduction throughthe oilon oil bearing strata itself. The rate of heat conduction is quite lowand, since the oil is being continuously raised to the surface, a greatdeal of-the.

applied heat is continuously carried away from the oilis arranged toutilize substantially all of the available is, thus, preventcd'frompenetrat-' tubing for pumping to the surface. This combinationofmicrowave energy penetration and thermal energy transfer provides agreater decrease in viscosity and, hence, a

greater rate of fluid flow for a given expenditure of input power thanhas heretofore been available.

,The microwave energy generating equipment of the invention is housed ina substantially tubular capsule secured to the lower end of the oil-wellproducing string. A portion of the capsule is made of stainless steelandv a portion is made of a strong reinforced plastic material. In aparticular embodiment of the invention, a plurality of microwavegenerators, such as magnetrons, are mounted in a vertically spacedrelationship within the plastic portion of the capsule. The magnetronsreceive their operating voltages by means of cables connected to a powersupply source stationed at the surface near the well head. The output.microwave power from the magnetron is radiated fromspeeially designedradiation cavities positioned inthe plastic portion of the capsule topro 7 vide an efficient transmission of energy into the oil-bearingformation.

The plastic portion is composedof a material that is substantiallytransparent to microwave energy. A circulating cooling system isprovided to carry thermal energy generated by the magnetrons to a heatex-,

sembly, so that any desired number of magnetrons, may be positionedalong the longitudinal axis of the well borein: accordance with aparticular desired application.

A suitable control system is utilized to actuatethe microwave energygeneration equipment whenever conditions at theoil-bearing formationwarrant the application of said energy to provide increased fluid flow.

, The structure of the invention can be utilized in openhole' completionwell bores or in closed-holecompletion.

well bores. For suitable microwave energy transmission, closedhole wellbores may utilizeliners fabricated from materials which aretransparentto microwave energy.

energy in two ways. First of all, microwave energy from a the R-Fgenerator source is caused to penetrate directly into the oil-bearingformation without being absorbed to any degree by the crude petroleumoil, or'gases present in the well bore and in the surrounding reservoir.This penetrating microwave energy heats the oil-bearing for- Thedetailed operation of the invention and the advan-- tages which accruetherefrom may be more. easily described with the help of theaccompanying drawings in which:

tion, or well head, of an oil well structure;

FIG. 1B showsavertical sectionview of the lower portion of 'anoilswellstructure, utilizing the microwave heating device of the inventionlocated within the well bore of said oil well'structure and shown inelevation therein;

FIG. 2 shows an elevation view of one embodiment of the microwaveheating capsule of the invention that is utilized in the oil-wellconstruction of FIG. 1B;

FIG. 3 shows a cut-away pictorial view of one microwave generatingsection of the microwave heating device of FIGS. 1 and 2;

FIG. 4 shows a sectional view along the line 4--4 of the radiationcavity of the structure shown in FIG. 3;

Patented Feb. 23, 1965 FIG. 1A shows a vertical section view of theupper poropen hole-type utilizing a well bore 11 having a steel tubing14 extends to the, well head 15 positioned'at the surface of the earth.The upper section of the well bore near the Well head shown in FIG. 1Ais shown slightly enlargedwith respect to the lower section shown inFIG.

1B so that well head 15. may be more clearly described I in laterparagraphs.

Ar'nicrowave heating capsule 18, which constitutes one:

embodiment of the invention, is secured to the lower end of pump tubing14. Microwave heating capsule 13 contains microwave generatingequipment, 'a heat exchange system, and associated electrical cablingand mechanical support means, all of which are described in more detailwithreference to FIGS. 2-4. A ground based power supply 19 is positionednear well head 15. Power supply 19 delivers high voltage rectifiedcurrent and AC. heater voltage. for the microwave generating equipmentas well as auxiliary voltages for operating associated electrical andelectromechanical equipment that may be utilized in capsule 18. Thesevoltagesare connected from power supply 19 to the equipment in thecapsuleby a high voltage D.C. cable 20 and low voltage AIC; cable 21which extenddownward through well bore ll. Cables 20 and 21 may besecured to pump tubing 14 byclamps 22 suitably spaced along the lengthof the well bore.

Oil-producing formation 13, which may vary in thickness overrelativelywide limits, is generally composed of a porous core material,such as limestone or sand stone, permeated with crude petroleum in aliquid or gaseous state. The liquid petroleum is brought to the surfacethrough tubing 14 by a conventional pumping system including a pump 67connected to a sucker rod may extend therethrough. A plurality of dogsare positioned in housing 29 and enclose pump tubing 14, as isWell-known in the art. A pair of pipes 31 opening into housing 29 areused to carry away the petroleum gases which rise to the surface from.oil-bearing formation 13. To prevent the gases from 'es caping out thetop of well head assembly 15, packing material 32 is placed around pumptubing 14 above dogs 30. Packing material 32 is held in place by a brasscover 33, the packing material and cover assembly beingcompressed bywell head cap 34 p which is threaded tightly onto housing 29. Suitableopenings are drilled through cover 33, packing material '32, dogs 30 andhousing 29 to allow cables 20 and21 and pump tubing 14 to extenddownward through well head assembly 15 into well bore 11.

FIG. 2 showsthe exterior of microwave heating capsule 18 which isconnected to the lower portion of producing string 14 by fiangeconnection 35. The upper portion of capsule 18 comprises a stainlesssteel tubing 36 having the same diameter as pump tubing 14 and havingperforations 37 drilled therein for allowing the petroleum products toenter pump tubing 14 as explained in more detail later. Upper cylinder36 has heat exchange coils, shown in FIG.I5, positioned therein. Fables20 and 21 are shown running along the length of andexternal to cylinder35. Section 88 of the lower portion of capsule 63 which extends upwardto a reciprocal motive means 7 (not shown) as is Well knownin theart.

In order to preventlateralmotion of'pump tubing'llt and capsule 18within well bore 1 1, co'nventional centralizers 23 are placed atsuitable points along the well bore. In order'to prevent longitudinalmotion in the pump tubing and capsule, an anchor assembly 24is'positioned at a suitable distanceabove capsule Anchor: assembly 24utilizes a plurality of movable dogs positioned at each end ofanchorhousing 66'. When the pump tubingaand capsule assembly have. beenlowered to their correct positions with respect to oil-bearingfor mation13, the tubing and capsule assembly are rotated Within the well bore.This rotation causes cam surfaces (not shown) within the anchor housing'65 to move dogs 25 outwardly so that teeth located on the outersurfaces of the dogs encounter and grip the inner walls of well casing12 to hold the tubing and capsule firmly in place in the well bore. Sucha construction isgenerally wellknown to those in theart. V

In order to facilitate assembly of the'arichorsection to pump tubing 14and to prevent damage to cables 20 and 21 during assembly, a pair offlange 'connections z aroused at each end of anchor assembly 24. -High'vo'lt age cable 2t) enters anchor housing 66 through an angularly boredhole 27 in the upper conic section of the housing and passes through thecenter tubing lof the housing and out the other 'end through a 'secondangularly bored hole 28. in the lower conic section of the housing. Lowvoltage cable 21 passes through openings between dogs25. v

At the upper end of well bore 1 1, well head assembly 15 is used to'deliver to suitable storage containers the crude petroleum productsthat are being-pumped from' Well head assembly15 comprises a housing 29having a cir the petroleum-bearing reservoir to the surface.

cular aperture at its lower end so that pump tubing 14 18 is made ofstainless steel and has a diameter larger than that of cylinder 36Section"88 houses a pump for circulating the fluid used in the heatexchange system of the. capsule. in the particular embodiment of FIG. 2,

there are shown three microwave heating sectionsBS,

These sections contain microwave generators, such as magnetrons or otherdevices capable of producing high frequency electromagneticenergy. Theportion of the capsule housing the microwave energy generators is madeof asuitable plastic material, suchasFibe'rglas, which allows microwaveenergy to be passed therethrough without loss to oil-bearing formation13.

38 may be utilized for a particularly desired application. A stainlesssteel nose cone 39 is secured to thebottom magnetron section to completethe capsule. Descripgenerating section 38 of capsule Each of themicrowave generating sections utilized in the capsule is fabricated insubstantiallythe s'ame'm'a'nner asthe one shown in FIG. 3. Magnetronsections 33 are housed within the plastic portion of capsule 13 showninFIG. 3 as plastic shell 69. Each section comprises aluminum structures70! t and 71 which are joined together bya flange connection 72,. Theupper end of structure 7ll'als'o has a flange connector'euwhich joins itto the next higher magnetron section positioned directly above. Thelower end of structure 71 has a solid flangeconnec'tor. 89 which is usedto join it to thenext lower. magnetron section positioned directlybelow. Solid flange connector 89 prevents the passage of microwave,energy into the succeeding section positioned directly below the sectionillustrated. Each of the flangeconnectionshas a plurality ofindentations 73"a'bout its periphery to allowthe electrical cabling andtubing for the heat exchange system to pass downward along the capsule.The bottommost magnetron section is joined to nose cone 3 9. A heatertransformer 41 having a pair of input terminals (not shown) to which areconnected wires 74 and 75 from low V voltage A.C. cable 21'is mounted tostructure 70 by means of brackets 47 bolted to structure 70 (bolts notshown) and to transformer 40. Apair of output terminals76- and 77mounted at the lower end 'of heater transformer 40 are connected tocathode heater terminals'el and 42 by apair of wires'78 and 79.A'cathode insulating Accordingly, by 7 this invention any number ofmicrowave heating sections ture for producing the required radiatingenergy.

vacuum seal 44 is shown having cooling fins 45 and 91 mounted thereupon.

The anode section of the magnetron (not specifically shown herein) isencompassed by a permanent magnet 49 and has a radiating antenna 50extending from the lower end thereof inside a dielectric vacuum seal 82.

The magnetron is held in place at each end by rubber blocks 51 toprevent unwarranted shock or vibration of the magnetron.

Radiating antenna 50 radiates into a radiation cavity 52 which comprisesthe lower portion of the inner aluminum structure 71. Radiation cavity52 has a plurality of longitudinal slots 53 which radiate the microwaveenergy that is generated out through the plasticshell 69 of capsule 18.In this particular embodiment, slots 53 are substantially symmetricallyspaced around the periphery of radiation cavity 52.

The lower portion of structure 71 which forms cavity 52 and has slots 53therein comprises a resonant struc- In order to provide a transfer ofthe radiating energy to the petroleum-bearing formation through thelongitudinal arrangement of slots 53 shown here, a plurality of probes85 are mounted adjacent each slot, as shown mos-t clearly in FIG. 4.Probes 85 project inwardly toward the center of cavity 52. It isdesirable that the transfer of energy be as efficient as possible byproviding a proper impedance match of the radiating system to thepetroleum-bearing formation into which the energy is directed. Theimpedance match depends generally on the dimensions of the slot and themake-up of the materials present in the formation. An empirical methodof determining the dimensions of the slot may be utilized by radiatingenergy from the microwave-generation system of the device into a sampleof the material that it is expected will be encountered in the actualoperation of the device and thereby determining the optimum values forthe slot dimensions on the basis of experimental measurements of theenergy obtained thereby.

High voltage D.C. cable 20 may be connected directly to the cathode ofthe magnetron or it may be connected, as shown, by a wire 92 to theappropriate transformer terminal 76, and, thence, to the cathode bymeansof wire 78.

The heat exchange system of the capsule is essentially a seriesconnection of tubes through which a suitable coolant is circulated(shown and described more clearly with reference to FIG. 5). In FIG. 3the cooled liquid is pumped downward through tubing 56 shown at the leftand enters the anode section at the right. The coolant is circulatedabout the anode and emerges by way of tubing 79 as shown whence it isconveyed downward to the next magnetron section. A return line 57carries the heated coolant directly from the bottomrnost magnetron tothe heat exchanger located in the upper stainless steel tubing section36 of the capsule.

The cabling and heat exchange tubing are shown more clearly in theschematic diagram of FIG. 5. In that figure there are shown only fourvertically spaced magnetrons58-61 although any number ofmagnetrons maybe used, depending on the thickness of the oil bearing strata to beheated. The high voltage cable 20 is ar ranged to have a plurality ofungrounded high voltage leads contained therein, the required groundbeing obtained from the metallic structure of the pump tubing andcapsule. The magnetrons are arranged in this particular embodiment sothat eachsuccessive pair of magnetrons is supplied in parallel from oneof the plurality of high voltage leads within cable 20. For example,magnetrons 58 and 59 are supplied from high voltage lead 62 andmagnetrons 60 and 61 are supplied in parallel from high voltage lead 63.Cable 21 is used to supply excitation voltage for the A.C. heatertransformers 40. In the embodiment shown, all of the heater transformersassociated with the magnetrons are supplied in parallel with voltagefrom the single two-wire A.C. cable 21.

The heat exchange system utilizes a series connection of tubing whereinthe cooled fluid is carried down tubing 56 into the anode section of thefirst magnetrons and, thence, to the anode section of the nextmagnetron, and so on. Return tubing 57 then carries the heated fluidback to the heat exchange coils 64 located in perforated cylinder 36 ofcapsule 18. A suitable pumping mechanism 65 is used to pump the coolingfluid throughout the closed cooling system. The coolant used may bewater or otherfluid suitable for such a purpose. A suitable seal 99 isshown between the heat exchange section and the magnetrons.

FIG. 6 shows a more detailed schematic diagram of the wiring of FIG. 5.For clarity only three magne-trons are shown and it is clear that thewiring scheme may be extended to include a greater number of magnetronsif desired. In the figmre, power supply 19 has a DC. high voltage supplyand an A.C. heater voltage supply 96 located at the earths surface.Cable 20 carries a plurality of high voltage leads, such as leads 62 and63 having a negative voltage thereon, the positive side of supply 95being grounded. Lead 62 has a first wire 97 connected to the cathode ofmagnetron 58 and a second wire 98 connected to magnetron 59. A.C. cable21 is connected in parallel from supply 96 to the primaries oftransformers 40, the secondaries of which are connected to the heater ofthe magnetrons. Lead 63 is connected to the cathode of magnetron 61 andthe anodes of each of the magnetrons are suitably grounded as mentionedabove.

It is generally desirable that the atmosphere within the capsule be ofsuch a nature as to substantially prevent the formation of moisture andto provide relatively good electrical insulation. For this purpose, asubstantially pure nitrogen atmosphere is used within the capsule and isinserted through plug 100 as shown in the drawings.

As can be seen with reference to FIGS. 1-4, application of the operatingvoltages to the magnetrons. causes microwave energy to be radiated fromthe vertically spaced radiating cavities 52 associated with eachmagnetron into oil-bearing formation 13. By microwave energy is meantenergy having a frequency within a range of from about 1000 megacyclesto 300,000 megacycles. In one particular embodiment of the invention, ithas been found that a suitable frequency of approximately 2500 mc. maybe used. The petroleum products which are present in the well bore andwhich permeate the formation absorb very little of the microwave energywhich penetrates the formation, substantially all of the energy beingabsorbed by the core material. The temperature rise within the formationcauses a drop in the viscosity of the petroleum products and, hence,increases their rate of flow from the formation into the producingstring as they enter through perforations 37 at the upper portion 36 ofcapsule 18. The petroleum is further heated by heat exchange coils 64over which it passes and a further decrease in viscosity of thepetroleum occurs. This additional decrease in viscosity, due to theapplication of thermal energy to the crude petroleum, provides a furtherincrease in its rate of flow. It can be seen that the system of theinvention utilizes both the microwave energy and thermal energygenerated by the magnetrons to increase the rate of flow of crudepetroleum products to the surface. It is obvious that the rate of fluidflow may be controlled by controlling the magnitude of the appliedmicrowave energy and the times at which the microwave generators areactuated.

It is also clear that the microwave heating device of the invention maybe utilized in a closed-hole oil-well structure. In that application,the opening in the oilbearing formation 13 may be lined with a strongperf0-- rated plastic liner which is transparent to microwave energy.Alternatively, the hole may be lined with a stainless steel liner havingsuitably placed radiation slots or:

openings madetherein for passage of the energy into the oil-bearingformation.

The particular embodiment shown and described with reference to FIGS.1-5 does not represent the only embodiment of the invention.Modifications will occur to those skilled in the art within the scope ofthe invention. Hence, the invention is notto be construed to' theparticular embodiment disclosed herein except as defined by the appendedclaims.

What is claimed is:

1. An apparatus for heating a petroleum-hearing formation and adapted tobe connected to the lower extremity of a producing string at a positionopposite said formation, said apparatus comprising a capsule havingfirst and second portions, said first portion of said capsule containinga plurality of electrical devices mounted therein for simultaneouslygenerating microwave energy and thermal energy, means for supplyingexcitation voltage to said devices, means for directing said microwaveenergy at a frequency of between 1000 and 300,090 megacycles into saidpetroleum-bearing formation, said second portion of said capsule havingperforations therein for allowing petroleum products to enter saidproducing string,,means for connecting said capsule to said producnigstring, said second capsule portion including a heat exchangerpositioned therein, means for carrying said thermal energy from saidmicrowave generating devices to said heat exchanger for heating saidpetroleum products entering said producing string through saidperforated portion of said capsule.

2. An apparatus for. heating a petroleum-bearing formation and adaptedto be connected to the lower extremity of a producing string at aposition opposite said formation, said apparatus comprising a capsulehaving first and second portions, said first portion of said capsulecontaining a plurality of electrical devices mounted therein forsimultaneously generating microwave energy and thermal energy, means forsupplying excitation voltages to said devices, resonant cavity means fordirecting said microwave energy into said petroleum-bearing formation,said second portion of said. capsule having perforations therein forallowing petroleum products to enter said producing string, means forconnecting said capsule to said producing string, said second capsuleportion including a heat exchanger positioned therein, means forcarrying said thermal energy from said microwave generating devices tosaidheat exchanger for heating said petroleum products entering saidproducing string through said perforated portion of said capsule.

3. An apparatus for heating a petroleum-hearing formation andadapted tobe connected to the lower extremity of a producingstring at apositionopposite said formation, said apparatus comprising a capsule havingfirst and second portions, saidfirst portion of said capsule containingaplurality of electrical devices mounted therein for simultaneouslygenerating microwave energy and thermal energy, means for supplyingexcitation voltages to said devices, a resonant cavity having aplurality of slots, means for directing said microwave energy into saidresonant cavity, whereby said microwave energy is directed outwardthrough said slots into said petroleum-bearing formation, said secondportion of said capsule having perforations therein for allowingpetroleum products to enter said producing string, means for connectingsaid capsule to-said producing string, said second capsule por tionincluding a heat exchanger positioned therein, means for carrying saidthermal energy from said microwave generating devices to said heatexchanger for heating said petroleum products entering said producingstring through said perforated portion of said capsule.

4. An apparatus for heating a petroleum-bearing formation and adapted tobe connected to the lower extremity of a producing string at a positionopposite said formstion, said apparatuscomprising a capsule having firstand "second portions, said first portion of said capsule containing aplurality of electrical devices'mounted therein for simultaneouslygenerating microwave energy and ther- 'mal energy, means for supplyingexcitation voltages to said devices, a resonant cavity having vaplurality of symmetrically spaced longitudinal slots, meansfor'directing said microwave energy into said resonant cavity wherebysaid microwave energy is directed outward through said slots into saidpetroleum-bearing formation, said second portion of said capsule havingperforations therein for allowing petroleum products to enter saidproducing string, means for connecting said capsule to said producingstring, said second capsule portion including a heat exchangerpositioned therein, means for carrying said thermal energy from saidmicrowave generating devices to said heat exchanger for heating saidpetroleum products entering said producing string through saidperforated portion of said capsule.

5. An apparatus for heating a petroleum-bearing formaation and adaptedto be connected to the lower extremity of a producing string at aposition opposite said formation, said apparatus comprising a capsulehaving first and second portions, said first portion of said capsulecontaining a plurality of electrical devices mounted therein forsimultaneously generating microwave energy and thermal energy, means forsupplying excitation voltages to said devices, a resonant cavity havinga plurality of symmetricallyspaced longitudinal slots, said slots havingselected dimensions for substantially providing an impedance matchbetween said resonant cavity and said petroleumbearing formation, meansfor directing said microwave energy into said resonant cavity wherebysaid microwave energy is directed outward throughsaid slots into saidpetroleum-bearing formation, said second portion of said capsule havingperforations therein for allowing petroleum products to enter saidproducing string, means for connecting said capsule to said producingstring, said second capsule portion including a heat exchangerpositioned therein, means for carrying said thermal energy from saidmicrowave generating devices to said heat exchanger for heating saidpetroleum products entering said producing string through saidperforated portion of said capsule.

6. An apparatus for heating a petroleum-bearing formation and adapted tobe connected to the lower extremity of a producing string at a positionopposite said formation, said apparatus comprising a capsule havingfirst and second portions, said first portion of said capsule containinga plurality of electrical devices mounted therein for simultaneouslygenerating microwave energy and thermal energy, power supply meanspositioned on the earths surface near the upper extremity of saidproducing string for producing operating voltages for said electrical devices, cabling means connected to said power supply and to said devices,means for directing said microwave energy into said petroleum-hearingformation, said second portion of said capsule having perforationstherein for allowing petroleum products to enter said producing string,means for connecting said capsule to said producing string, said secondcapsule portion including a heat exchanger positioned therein, means forcarrying thermal energy from said microwave generating devices to saidheat exchanger for heating said petroleum products entering saidproducing string through said perforated portion of said capsule.

'7. An apparatus for heating a petroleum-bearing formation and adaptedto be connected to the lower extremity of a producing string at aposition opposite said formation, said apparatus comprising a capsulehaving a first plastic portion and a second metallic portion, said firstplastic portion of said capsule containing a plurality of magnetronsmounted therein in a vertically spaced relationship for simultaneouslygenerating microwave energy and thermal energy, means for directing saidmicrowave energy into said petroleum-bearing formation, said second"metallic portion of said capsule having perforations there r in forallowing petroleum products to enter said produc ing string, means forconnecting said capsule to said pro- 9 ducing string, said secondcapsule portion including a heat exchanger positioned therein, means forcarrying thermal energy from said magnetrons to said heat exchanger forheating said petroleum products entering said producing string throughsaid perforated portion of said capsule.

8. An apparatus for heating a petroleum-bearing formation and adapted tobe connected to the lower extremity of at producing string at a positionopposite said formation, said apparatus comprising a capsule having afirst plastic portion and a second metallic portion, said first plasticportion of said capsule containing a plurality of magnetrons mountedtherein in a vertically spaced relationship for simultaneouslygenerating microwave energy and thermal energy, structure means forproviding a plurality of radiation cavities, said structure means havinga plurality of vertical slots for directing said microwave energy intosaid petroleum-bearing formation, said second metallic portion of saidcapsule having perforations therein for allowing petroleum products toenter said producing string, means for connecting said capsule to saidproducing string, said second capsule portion including a heat exchangerpositioned therein, means for carrying thermal energy from saidmagnetrons to said heat exchanger for heating said petroleum productsentering said producing string through said perforated portion of saidcapsule.

9. An apparatus for heating a petroleum-bearing formation and adapted tobe connected to the lower extremity of a producing string at a positionopposite said formation, said apparatus comprising a capsule having afirst plastic portion and a second metallic portion, said first plasticportion of said capsule containing a plurality of magnetrons mountedtherein a vertically spaced relation ship for simultaneously generatingmicrowave energy and thermal energy, means for directing said microwaveenergy into said petroleum-bearing formation, said second metallicportion of said capsule having perforations therein for allowingpetroleum products to enter said producing string, means for connectingsaid capsule to said producing string, said second capsule portionincluding a heat exchanger positioned therein, series connected tubingmeans surrounding the anode portions of said magnetrons and connected tosaid heat exchanger, means for circulating a coolant through said tubingmeans whereby thermal energy is carried from said microwave generatingdevices to said heat exchanger for heating said petroleum productsentering said producing string through said perforated portion of saidcapsule.

10. An apparatus for heating a petroleum-bearing formation and adaptedto be connected to the lower extremity of a producing string at aposition opposite said formation, said apparatus comprising a capsulehaving a first plastic portion and a second metallic portion, said firstportion of said capsule containing a plurality of microwave generatingdevices mounted therein for simultaneously generating microwave energyand thermal energy, a power supply for producing high potential and lowpotential operating voltages for said devices, a first cable connectedfrom said power supply to said devices for transmitting said highpotential operating voltages, said first cable having a plurality ofhigh potential leads connected to a plurality of pairs of parallelconnected devices, a single common ground connection associated withsaid high potential leads, a second cable connected from said powersupply to said devices for transmitting said low potential operatingvoltages, said devices being connected in parallel to said low potentialcable, means for directing said microwave energy into saidpetroleumbearing formation, said second portion of said capsule havingperforations therein for allowing petroleum products to enter saidproducing string, means for connecting said capsule to said producingstring, said second capsule portion including a heat exchangerpositioned therein, means for carrying thermal energy from saidmicrowave generating devices to said heat exchanger for heating saidpetroleum products entering said producing string through saidperforated portion of said capsule.

References Cited in the file of this patent UNITED STATES PATENTS1,169,262 Huff Jan. 25, 1916 1,291,302 Waring Jan. 14, 1919 1,457,479Wolcott June 5, 1923 2,186,035 Niles Ian. 9, 1940 2,455,941 Muskat et alDec. 14, 1948 2,455,942 Coggeshall et al Dec. 14, 1948 2,585,970 ShawFeb. 19, 1952 2,632,868 Hull Mar. 24, 1953 2,685,930 Albaugh Aug. 10,1954 2,742,967 Carpenter Apr. 24, 1956 2,757,738 Ritchey Aug. 7, 19562,816,735 Dalinda et al. Dec. 17, 1957 2,911,047 Henderson Nov. 3, 1959

1. AN APPARATUS FOR HEATING A PETROLEUM-BEARING FORMATION AND ADAPTED TOBE CONNECTED TO THHE LOWER EXTREMITY OF A PRODUCING STRING AT A POSITIONOPPOSITE SAID FORMATION, SAID APPARATUS COMPRISING A CAPSULE HAVINGFIRST AND SECOND PORTIONS, SAID FIRST PORTION OF SAID CAPSULE CONTAININGA PLURALITY OF ELECTRICAL DEVICES MOUNTED THEREIN FOR SIMULTANEOUSLYGENERATING MICROWAVE ENERGY AND THERMAL ENERGY, MEANS FOR SUPPLYINGEXCITATION VOLTAGES TO SAID DEVICES, MEANS FOR DIRECTING SAID MICROWAVEENERGY AT A FREQUENCY OF BETWEEN 1000 AND 300,000 MEGACYCLES INTO SAIDPETROLEUM-BEARING FORMATION, SAID SECOND PORTION OF SAID CAPSULE HAVINGPERORATIONS THEREIN FOR ALLOWING PETROLEUM PRODUCTS TO ENTER SAIDPRODUCING STRING, MEANS FOR CONNECTING SAID CAPSULE TO SAID PRODUCINGSTRING, SAID SECOND CAPSULE PORTION INCLUDING A HEAT